This invention relates generally to the art of electronic sound transmission, recording and reproduction, and, more specifically, to improvements in surround sound techniques.
Improvements in the quality and realism of sound reproduction have steadily been made during the past several decades. Stereo (two channel) recording and playback through spatially separated loud speakers significantly improved the realism of the reproduced sound, when compared to earlier monaural (one channel) sound reproduction. More recently, the audio signals have been encoded in the two channels in a manner to drive four or more loud speakers positioned to surround the listener. This surround sound has further added to the realism of the reproduced sound. Multi-channel (three or more channel) recording is used for the sound tracks of most movies, which provides some spectacular audio effects in theaters that are suitably equipped with a sound system that includes loud speakers positioned around its walls to surround the audience. Standards are currently emerging for multiple channel audio recording on small optical CDS (Compact Disks) that are expected to become very popular for home use. A recent DVD (Digital Video Disk) standard provides for multiple channels of PCM (Pulse Code Modulation) audio on a CD that may or may not contain video.
Theoretically, the most accurate reproduction of an audio wavefront would be obtained by recording and playing back an acoustic hologram. However, tens of thousands, and even many millions, of separate channels would have to be recorded. A two dimensional array of speakers would have to be placed around the home or theater with a spacing no greater than one-half the wavelength of the highest frequency desired to be reproduced, somewhat less than one centimeter apart, in order to accurately reconstruct the original acoustic wavefront. A separate channel would have to be recorded for each of this very large number of speakers, involving use of a similar large number of microphones during the recording process. Such an accurate reconstruction of an audio wavefront is thus not at all practical for audio reproduction systems used in homes, theaters and the like.
When desired reproduction is three dimensional and the speakers are no longer coplanar, these complications correspondingly multiply and this sort of reproduction becomes even more impractical. The extension to three dimensions allows for special effects, such as for movies or in mastering musical recordings, as well as for when an original sound source is not restricted to a plane. Even in the case of, say, a recording of musicians on a planar stage, the resultant ambient sound environment will have a three dimensional character due to reflections and variations in instrument placement which can be captured and reproduced. Although more difficult to quantify than the localization of a sound source, the inclusion of the third dimension adds to this feeling of “spaciousness” and depth for the sound field even when the actual sources are localized in a coplanar arrangement.
Therefore, it is a primary and general object of the present invention to provide techniques of reproducing sound with improved realism by multi-channel recording, such as that provided in the emerging new audio standards, with about the same number of loud speakers as currently used in surround sound systems.
It is another object of the present invention to provide a method and/or system for playing back recorded or transmitted multi-channel sound in a home, theater, or other listening location, that allows the user to set an electronic matrix at the listening location for the specific arrangement of loud speakers being used there.
It is further objective of the present invention to extend these techniques and methods to the capture and reproduction of a three dimensional sound field where the loud speakers are placed in a non-coplanar arrangement.